The invention relates to a flat illumination device which, in addition to an illumination function, also has a mirror function, i.e. the illumination device can also be used as a mirror which can be illuminated.
Illuminateable mirrors are usually produced by arranging one or more separate lights outside the actual mirror surface, for example to the side of or above the mirror surface. The generally small depth of a mirror ultimately cannot be put to good use on account of the dimensions of the separate light(s) used for the illumination. Suitable lights typically comprise at least one lamp, including the lamp holder and, if appropriate, associated lamp reflector, a light housing or a light cover and, when using discharge lamps, for example fluorescent lamps, additionally an electrical operating unit.
It is an object of the present invention to provide an improved illuminateable mirror.
This object is achieved by a flat illumination device, comprising a base plate and a front plate, which are connected to form an at least partially transparent vessel which, in its interior, has an ionizable fill, at least one of the two plates, in a partial region of the vessel, being at least partially provided with a mirror surface, and an unmirrored partial region of the vessel being designed to realize an illumination function. Particularly advantageous configurations are given in the dependent claims.
By contrast to the structure of conventional illuminateable mirrors comprising a plurality of separate components, which was outlined in the introduction, the invention proposes a flat illumination device with an integrated mirror surface.
The illumination device according to the invention is based on a flat lamp, comprising a base plate and a front plate, which are connected to form an at least partially transparent vessel which, in its interior, has an ionizable fill.
The connection may be produced, for example, by means of a frame which is arranged between the two plates and is connected thereto. In this way, the frame also defines the distance between the two substantially planar plates. The frame usually runs along the edge regions of both plates, in order that it be possible for the entire surface extent of both plates to be utilized as completely as possible to form the vessel.
The frame can be dispensed with if at least one of the two plates, in its edge region, is shaped with suitable convexity, so that the two assembled plates form a vessel even without a frame.
According to the invention, only a partial region of the vessel is designed to realize the illumination function. It is preferable for this partial region to extend along at least a part of the edge region of the vessel. In the remaining region of the vessel, at least one of the two plates is at least partially provided with a mirror surface.
Optionally, the vessel may also be divided into two or more chambers which separate the regions of the flat illumination device which are designed for the mirror and illumination functions from one another. In this way, it is possible to restrict the ionizable fill to the region which is designed for the illumination function, i.e. for only the corresponding chamber(s) to be filled with the ionizable fill which is provided for the discharge. This is advantageous in particular when using relatively expensive fills, for example xenon. The chamber which surrounds the mirror surface may be filled with a less expensive gas (mixture), for example nitrogen or dried air.
The flat lamp of the illumination device according to the invention is particularly preferably of the dielectric barrier discharge lamp type. In this type of flat lamp, at least some of the electrodes are separated from the fill of the discharge vessel by a dielectric. For this purpose, the electrodes are arranged either on the outer surface of the discharge vessel, as disclosed in EP 0 839 436 B1, in which case the wall of the discharge vessel itself functions as said dielectric, or on the inner surface of the discharge vessel, in which case the electrodes are additionally covered with a dielectric layer, as disclosed in WO 98/43277. The electrodes are usually designed as structures which resemble conductor tracks and which are applied to the inner surface, for example by means of screen printing. In a similar way, the dielectric layer is printed onto these strip-like electrodes. For further details in this connection, reference is made to WO 99/66538.
This type of lamp is preferably operated in accordance with the pulsed operating method disclosed in EP 0 733 266 B1, since this has proven particularly efficient compared to the conventional method of operating these dielectric barrier discharges with a sinusoidal alternating voltage. In any event, the plurality of adjacent electrodes is selected to alternate. As a result, the discharge is lit in each case between adjacent electrodes.
A partial region of at least one of the two plates, for example a partial region of the inner surface of the base plate, is provided with the abovementioned mirror surface. While this mirrored partial region functions in a conventional way as a mirror, the unmirrored partial region is used to realize the illumination function, i.e. as a lamp. For this purpose, the unmirrored partial region is printed with the abovementioned electrode structure and the dielectric layer. In operation, the gas discharge takes place only in this partial region, generating the light required for the illumination function either on its own or in combination with a phosphor layer which has been applied to the wall of the discharge vessel.
A further advantage is that the illumination device is easy to clean, since the entire front side, i.e. the mirror region including lamp region, is delimited by the planar, single-piece front plate.
The surface area of the mirrored partial region typically corresponds to more than 50%, or better more than 60%, preferably more than 70%, particularly preferably more than 80% of the front surface of the front plate, in order, on the one hand, to be able to provide a mirror area which is sufficiently large for use with respect to the area required for the entire illumination device. On the other hand, the area of the unmirrored partial region which functions as a lamp must be sufficiently large to be able to ensure sufficient, shadow-free illumination which is as uniform as possible. In view of this requirement, it has proved appropriate if the surface area functioning as a lamp corresponds to more than 5%, or better approx. 10% or more of the front surface of the front plate.